Search Results (308)

Electrocoagulation (EC) processes have emerged as an efficient solution for different inorganic and organic effluents. The main characteristics of this versatile process are its ease of operation and low sludge production. The literature indicates that EC can be successfully used as a single process or a step within a combined treatment system. If used in a combined system, this process could be employed as a pre-, a post-, or middle treatment step. Additionally, the EC process has been used in both continuous and batch modes. In most studies, EC has achieved significant improvements in the treated water quality and relatively low total energy consumption. This review presents a comprehensive evaluation and analysis of standalone and combined continuous EC processes. The influence of key operational parameters on continuous EC performance is thoroughly discussed. Furthermore, recent advancements in reactor design, modeling, and process optimization are addressed. The benefits of integrating other treatment processes with the EC process, such as advanced oxidation, membranes, chemical coagulation, and adsorption, are also evaluated. The performance of most standalone and combined EC processes used for organic pollutant treatment and published in the last 25 years is critically analyzed. This review is expected to give researchers many insights to improve their treatment scenario with recent and efficient environmental experiences, sustainability, and circular economy. The clearly presented information is expected to guide researchers in selecting efficient, cost-effective, and time-saving treatment alternatives. The findings ensure the considerable potential of continuous EC treatment processes for organic pollutants. However, more research is warranted to enhance process design, operational efficiency, scale-up, and economic viability. Full article

Aquatic biomass—ranging from fish scales and crustacean shells to various algae species—offers an abundant, renewable source for carbon dot (CD) synthesis, aligning with circular economy principles. This review highlights recent studies for valorizing aquatic biomass into high-performance carbon-based nanomaterials—specifically aquatic biomass-based carbon dots (AB-CDs)—briefly summarizing green synthesis approaches (e.g., hydrothermal carbonization, pyrolysis, and microwave-assisted treatments) that minimize environmental impact. Subsequent sections highlight the varied applications of AB-CDs, particularly in biosensing (including the detection of marine biotoxins), environmental monitoring of water pollutants, and drug delivery systems. Physically AB-CDs show unique optical and physicochemical properties—tunable fluorescence, high quantum yields, enhanced sensitivity, selectivity, and surface bio-functionalization—that make them ideal for a wide array of applications. Overall, the discussion underlines the significance of this approach; indeed, transforming aquatic biomass into carbon dots can contribute to sustainable nanotechnology, offering eco-friendly solutions in sensing, environmental monitoring, and therapeutics. Finally, current challenges and future research directions are discussed to give a perspective of the potential of AB-CDs; the final aim is their integration into multifunctional, real-time monitoring and therapeutic systems—for sustainable nanotechnology innovations. Full article

Acid mine drainage (AMD) remains a critical environmental challenge in South Africa due to its severe impact on water quality, ecosystems and public health. Numerous studies on AMD management, treatment and resource recovery have been conducted over the past 20 years. This study presents a comprehensive review of research activities on AMD in South Africa from 1998 to 2025, highlighting key trends, emerging challenges and future directions. The study reveals a significant focus on passive and active treatment methods, environmental remediation and the recovery of valuable resources, such as iron, rare earth elements (REEs) and gypsum. A bibliometric analysis was conducted to identify the most influential studies and thematic research areas over the years. Bibliometric tools (Biblioshiny and VOSviewer) were used to analyse the data that was extracted from the PubMed database. The findings indicate that research production has increased significantly over time, with substantial contributions from top academics and institutions. Advanced treatment technologies, the use of artificial intelligence and circular economy strategies for resource recovery are among the new research prospects identified in this study. Despite substantial progress, persistent challenges, such as scalability, economic viability and policy implementation, remain. Furthermore, few technologies have moved beyond pilot-scale implementation, underscoring the need for greater investment in field-scale research and technology transfer. This study recommends stronger industry–academic collaboration, the development of standardised treatment protocols and enhanced government policy support to facilitate sustainable AMD management. The study emphasises the necessity of data-driven approaches, sustainable technology and interdisciplinary cooperation to address AMD’s socioeconomic and environmental effects in the ensuing decades. Full article

Construction and demolition byproducts include substantial amounts of wood panel waste (WPW) that pose environmental challenges. They also create opportunities for sustainable resource recovery. This study investigates the potential of WPW-derived biochar as an efficient adsorbent for phenol removal from aqueous solutions. Biochar was produced via pyrolysis at 450 °C and subsequent activation at 750, 850, and 950 °C. The biochar’s physicochemical properties, including surface area, pore volume, and elemental composition, were characterized using advanced methods, including BET analysis, elemental analysis, and adsorption isotherm analysis. Activated biochar demonstrated up to nine times higher adsorption capacity than raw biochar, with a maximum of 171.9 mg/g at 950 °C under optimal conditions: pH of 6 at 25 °C, initial phenol concentration of 200 mg/L, and biochar dosage of 1 g/L of solution for 48 h. Kinetic and isotherm studies revealed that phenol adsorption followed a pseudo-second-order model and fit the Langmuir isotherm, indicating chemisorption and monolayer adsorption mechanisms. Leaching tests confirmed the biochar’s environmental safety, with heavy metal concentrations well below regulatory limits. Based on these findings, WPW biochar offers a promising, eco-friendly solution for wastewater treatment in line with circular economy and green chemistry principles. Full article

The food industry consumes large amounts of water across various processes, and generates wastewater characterized by parameters like biochemical oxygen demand, chemical oxygen demand, pH, suspended solids, and nutrients. To meet environmental standards and enable reuse or valorization, treatment methods such as physicochemical, biological, and membrane-based processes are applied. This review focuses on the valorization of food industry wastewater in the biotechnological production of high-value products, with an emphasis on starch-rich wastewater, wineries and confectionery industry wastewater, and with a focus on new technologies for reduces environmental burden but also supports circular economy principles. Starch-rich wastewaters, particularly those generated by the potato processing industry, offer considerable potential for biotechnological valorization due to their high content of soluble starch, proteins, organic acids, minerals, and lipids. These effluents can be efficiently converted by various fungi (e.g., Aspergillus, Trichoderma) and yeasts (e.g., Rhodotorula, Candida) into value-added products such as lipids for biodiesel, organic acids, microbial proteins, carotenoids, and biofungicides. Similarly, winery wastewaters, characterized by elevated concentrations of sugars and polyphenols, have been successfully utilized as medium for microbial cultivation and product synthesis. Microorganisms belonging to the genera Aspergillus, Trichoderma, Chlorella, Klebsiella, and Xanthomonas have demonstrated the ability to transform these effluents into biofuels, microbial biomass, biopolymers, and proteins, contributing to sustainable bioprocess development. Additionally, wastewater from the confectionery industry, rich in sugars, proteins, and lipids, serves as a favorable fermentation medium for the production of xanthan gum, bioethanol, biopesticides, and bioplastics (e.g., PHA and PHB). Microorganisms of the genera Xanthomonas, Bacillus, Zymomonas, and Cupriavidus are commonly employed in these processes. Although there are still certain regulatory issues, research gaps, and the need for more detailed economic analysis and kinetics of such production, we can conclude that this type of biotechnological production on waste streams has great potential, contributing to environmental sustainability and advancing the principles of the circular economy. Full article

This work studies and analyzes the transition from a linear to a circular economy through wastewater treatment and resource recovery. As wastewater volumes grow, sustainable management becomes critical. This study highlights the reuse of treated effluent, beneficial sludge utilization, and energy generation via anaerobic digestion. Wastewater treatment plants should be envisioned as hubs for recovering water, materials, and energy, rather than disposal facilities. Emphasizing resource efficiency, the circular economy approach offers viable solutions to challenges related to resource scarcity, climate change, and ecological impact. Full article

Biodegradable polymer composites offer promising alternatives to petroleum-based plastics, supporting the principles of a zero waste and circular economy. This study investigates the reinforcing potential of alkali-treated wood flour derived from recycled pine (Pinus brutia Ten.) and poplar (Populus alba L.) waste wooden pallets in poly(lactic acid) (PLA) biocomposites. Wood flour was initially recovered through grinding and screening during recycling, followed by alkali treatment via a green chemistry approach to enhance interfacial bonding with the PLA matrix. The impact of alkali concentration and two fabrication methods—additive manufacturing (AM) and injection molding (IM)—on the properties of developed biocomposite materials was assessed through mechanical, physical, morphological, and thermal analyses. IM samples outperformed AM counterparts, with the IM PLA containing 30 wt% wood flour (alkali-treated with 10% solution) showing the highest mechanical gains: tensile (+71.35%), flexural (+64.74%), and hardness (+2.62%) compared to untreated samples. Moreover, the AM sample with 10 wt% wood flour and 10% alkali treatment showed a 49.37% decrease in water absorption compared to the untreated sample, indicating improved hydrophobicity. Scanning electron microscopy confirmed that alkali treatment reduced void content and enhanced morphological uniformity, while thermal properties remained consistent across fabrication methods. This work introduces a green composite using non-toxic materials and treatments, facilitating eco-friendly production aligned with zero waste and circular economy principles throughout the manufacturing lifecycle. Full article

The loss of hectares of forest areas has become a global issue that has worsened over recent years due to unsustainable human activities. In a context of limited availability of productive land, it is urgent to adopt efficient strategies to recover the affected natural areas. Actions based on a circular economy, such as the use of organic chemical matrices recovered from water waste treatment plant waste, have proven to be effective. In this regard, the addition of plant growth-promoting bacteria (PGPB), such as Bacillus pretiosus and Pseudomonas agronomica, can contribute to the chemical treatment, favoring the recovery of soils, accelerating the recovery of vegetation cover, and inducing an increase in biodiversity. In this research, the effect of bio-fertigation under controlled laboratory conditions in Quercus pyrenaica is evaluated. After a thirty-six-week trial, the biometric and nutritional parameters of the plants were harvested and measured, and the diversity and composition of the metagenomes of their rhizospheres were evaluated. As well, the cenoantibiogram and the metabolic diversity were measured. The results showed that the use of these biofertilizers increased the variables related to plant production, quality of plant composition as an indirect means of their resilience, as well as an increase in rhizospheric microbial diversity and a reduction in their MIC resistance to the most widely used antibiotics. For all these reasons, the use of the biofertilizer result of the combination of WWTP waste, Bacillus pretiosus, and Pseudomonas agronomica is postulated as an environmentally friendly strategy that can contribute to the recovery of potential oak forest areas. Full article

As sensitive parts of the water treatment process, reverse osmosis (RO) membranes are the most important for desalination and wastewater treatment. But the performance of RO membranes deteriorates over time due to fouling, necessitating frequent replacements. One of the environmental challenges is the disposal of End-of-Life (EoL) RO membranes, which are made of non-biodegradable polymers. The reuse of EoL membranes as a sustainable approach for waste saving and resource efficiency has recently attracted considerable attention. The present work provides a comprehensive overview of the strategies for reusing EoL RO membranes as sustainable alternatives to conventional disposal methods. Furthermore, the fundamental principles of RO technology, the primary types and impacts of membrane fouling, and advanced cleaning and regeneration techniques are discussed. The conversion of EoL membranes into nanofiltration (NF), ultrafiltration (UF), and forward osmosis (FO) membranes is also covered in this review, as well as their uses in brackish water desalination, dye/salt separation, groundwater treatment, and household wastewater reuse. Environmental and economic benefits, as well as technical, social, and regulatory challenges, are also discussed. Finally, the review highlights innovative approaches and future directions for incorporating EoL membrane reuse into circular economy models, outlining its potential to improve sustainability and reduce operational costs in water treatment systems. Full article

Plastic waste and water pollution demand circular economy-driven innovations. This review examines metal–organic framework (MOF) synthesis from polyethylene terephthalate (PET) waste for wastewater treatment. Depolymerized PET yields terephthalic acid and ethylene glycol—essential MOF precursors. We evaluate the following: (1) PET depolymerization (hydrolysis, glycolysis, ammonolysis) for monomer recovery efficiency; (2) MOF synthesis (solvothermal, microwave, mechanochemical) using PET-derived linkers; (3) performance in adsorbing heavy metals, dyes, and emerging contaminants. PET-based MOFs match or exceed commercial adsorbents in pollutant removal while lowering costs. Their tunable porosity and surface chemistry enhance selectivity and capacity. By converting waste plastics into functional materials, this strategy tackles dual challenges: diverting PET from landfills and purifying water. The review underscores the environmental and economic benefits of waste-sourced MOFs, proposing scalable routes for sustainable water remediation aligned with zero-waste goals. Full article

The environmental impact of first-generation biodiesel production, particularly deforestation and soil degradation caused by palm and soybean cultivation, has raised concerns about sustainability. In contrast, second-generation biodiesel utilizes waste as feedstock, offering a more sustainable alternative. Used cooking oil (UCO), a significant waste stream, represents a viable feedstock for biodiesel production, reducing pollution and mitigating economic, environmental, and social challenges. While Europe has demonstrated successful UCO waste management strategies, many regions lack efficient systems, leading to improper disposal that causes water eutrophication, soil degradation, and increased wastewater treatment costs. This study develops a comprehensive strategy for UCO management to optimize its energy potential in biodiesel production, using Barranquilla, Colombia, as a case study. Transesterification, identified as the most efficient conversion method, achieves conversion rates of up to 90%. A pilot project in the Barranquilla area estimates that 963,070.95 kg of UCO is generated annually, with the potential to produce 902,108.56 kg of biodiesel. These findings contribute to the advancement of circular economy principles, offering an adaptable framework for sustainable biofuel production in other regions. Full article

Broccoli stalks are considered an agro-industrial by-product that, in the context of fresh consumption, is undervalued, as only broccoli florets are typically marketed. This study evaluated the up-cycling of broccoli stalks into a value-added fresh-cut product through postharvest preservation strategies. Stalks were peeled, cut into sticks (8 × 8 mm × 50–100 mm), sanitised, packaged under modified atmosphere conditions, and stored at 5 °C. Treatments included (a) calcium ascorbate (CaAsc, 1% w/v), (b) trehalose (TREH, 5% w/v), (c) hot water treatment (HWT, 55 °C, 1 min), and several combinations of them. HWT alone was highly effective in reducing browning, a key factor for achieving an extended shelf-life, controlling microbial growth and respiration, and obtaining the highest sensory scores (appearance = 7.3 on day 11). However, it was less effective in preserving bioactive compounds. The HWT + CaAsc treatment proved to be the most effective at optimising quality and retaining health-promoting compounds. It increased vitamin C retention by 78%, antioxidant capacity by 68%, and total phenolic content by 65% compared to the control on day 11. This synergistic effect was attributed to the antioxidant action of ascorbic acid in CaAsc. TREH alone showed no preservative effect, inducing browning, elevated respiration, and microbial proliferation. Overall, combining mild thermal and antioxidant treatments offers a promising strategy to valorise broccoli stalks as fresh-cut snacks. An 11-day shelf-life at 5 °C was achieved, with increased content of health-promoting bioactive compounds, while supporting circular economy principles and contributing to food loss mitigation. Full article

The latest FAO report indicates that aquaculture accounts for 51% of the global production volume of fish and seafood. However, despite the continuous growth of this activity, there is evidence of the excessive use of groundwater in its production processes, as well as pollution caused by nutrient discharges into surface waters due to the water exchange required to maintain water quality in fishponds. Given this context, the objectives of this study were as follows: (1) to review which emergent and floating plant species are used in constructed wetlands (CWs) for the bioremediation of aquaculture wastewater; (2) to identify the aquaculture species whose wastewater has been treated with CW systems; and (3) to examine the integration of CWs with recirculating aquaculture systems (RASs) for water reuse. A systematic literature review was conducted, selecting 70 scientific articles published between 2003 and 2023. The results show that the most used plant species in CW systems were Phragmites australis, Typha latifolia, Canna indica, Eichhornia crassipes, and Arundo donax, out of a total of 43 identified species. These plants treated wastewater generated by 25 aquaculture species, including Oreochromis niloticus, Litopenaeus vannamei, Ictalurus punctatus, Clarias gariepinus, Tachysurus fulvidraco, and Cyprinus carpio, However, only 40% of the reviewed studies addressed aspects related to the incorporation of RAS elements in their designs. In conclusion, the use of plants for wastewater treatment in CW systems is feasible; however, its application remains largely at the experimental scale. Evidence indicates that there are limited real-scale applications and few studies focused on the reuse of treated water for agricultural purposes. This highlights the need for future research aimed at production systems that integrate circular economy principles in this sector, through RAS–CW systems. Additionally, there is a wide variety of plant species that remain unexplored for these purposes. Full article

The treatment of wastewater and the utilization of the by-products of these processes are an important part of the circular economy. The sewage sludge, a result of wastewater treatment, could be used as a material for plant nutrient supply and/or soil-improving products. The city of Nyíregyháza, Hungary, with 120,000 citizens, has a well-planned water treatment plant operated by Nyírségvíz Ltd., which, in cooperation with the Research Institute of Nyíregyháza, developed a municipal sewage sludge compost (SSC). The closed loop of sewage water treatment and the agricultural utilization of its by-product has been developed and managed. The compost product called Nyírkomposzt was planned for acidic sandy soils. Beyond the agronomic benefits, the sustainable and environmentally sound utilization of SSC reduces sewage sludge disposal. This active involvement of a water utility company demonstrates the potential of cross-sectoral cooperation in solving environmental problems. The quality of the compost fits the Hungarian legislation. To study the effects of 0, 9, 18, and 27 t ha⁻¹ doses of compost on acidic sandy soil, a long-term small plot experiment was started in 2003. The cumulative effects of the regular (every third year, last treatment before sampling in 2021) application of the SSC showed positive changes in basic soil properties, depending on the doses used. Increasing values were found in the case of pH from 4.5 to 6, plant available P₂O₅ from 240 to 690 ppm, and plant available K₂O from 180 to 200 ppm. The plant-available zinc and copper content also increased. Soil organic matter and total N content stabilized at around 0.9% and 0.08%, respectively. The grain yields of winter rye also increased in both investigated years. The yields of 18 t ha⁻¹ treatment were about two times higher compared to the control, but only in 2022 was the difference significant. Our findings underscore the potential of well-planned SSC applications to improve the fertility of ploughed, acidic sandy soil, taking into account the theory of the circular economy by utilizing wastes and decreasing landfilling. Full article

This study explores innovative strategies for decarbonizing sludge thermal treatments used in electrical power generation, with a focus on integrating sensor technologies and artificial intelligence. Sludge, a carbon-intensive byproduct of wastewater treatment, presents both environmental challenges and opportunities for energy recovery. The paper provides a comprehensive analysis of thermal processes such as pyrolysis, gasification, co-combustion, and emerging methods, including hydrothermal carbonization and supercritical water gasification. It evaluates their carbon mitigation potential, energy efficiency, and economic feasibility, emphasizing the importance of catalyst selection, carbon dioxide capture techniques, and reactor optimization. The role of real-time monitoring via sensors and predictive modeling through artificial intelligence (AI) is highlighted as critical for enhancing process control and sustainability. Case studies and recent advances are discussed to outline future pathways for integrating thermal treatment with circular economy principles. This work contributes to sustainable waste-to-energy practices, supporting global decarbonization efforts and advancing the energy transition. Full article